Communication devices such as wireless devices are also known as e.g. User Equipments (UEs), mobile terminals, wireless terminals and mobile stations. Wireless devices are enabled to communicate wirelessly in a cellular communication network, wireless communication network or wireless communications system, sometimes also referred to as a cellular radio system or a cellular network. The communication may be performed, e.g., between two wireless devices, between a wireless device and a regular telephone and/or between a wireless device and a server via a Radio Access Network (RAN), and possibly one or more core networks, comprised within the cellular communication network.
Wireless devices may further be referred to as mobile telephones, cellular telephones, laptops, or tablet computer with wireless capability, just to mention some further examples. The wireless devices in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another terminal or a server.
The cellular communication network covers a geographical area which is divided into cell areas, wherein each cell area being served by an access node such as a base station (BS), e.g., a Radio Base Station (RBS), which sometimes may be referred to as e.g. “evolved Node B”, “eNB”, “eNodeB”, “NodeB”, “B node”, “node B” or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as, e.g., macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the terminals within range of the base stations.
In some RANs, several base stations may be connected, e.g. by landlines or microwave, to a radio network controller, e.g. a Radio Network Controller (RNC) in Universal Mobile Telecommunications System (UMTS), and/or to each other. The radio network controller, also sometimes termed a Base Station Controller (BSC) e.g. in GSM, may supervise and coordinate various activities of the plural base stations connected thereto. GSM is an abbreviation for Global System for Mobile Communications (originally: Groupe Spécial Mobile). In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs, eNBs or even NBs, may be directly connected to other base stations and may be directly connected to one or more core networks.
The 3GPP LTE radio access standard has been written in order to support high bitrates and low latency both for uplink and downlink traffic. All data transmission is in LTE are controlled by the base stations.
UMTS is a third generation mobile communication system, which evolved from the GSM, and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for wireless devices. High Speed Packet Access (HSPA) is an amalgamation of two mobile telephony protocols, High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), defined by 3GPP, that extends and improves the performance of existing 3rd generation mobile telecommunication networks utilizing the WCDMA. Moreover, the 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies, for example into evolved UTRAN (E-UTRAN) used in LTE.
In the context of this disclosure, the expression Downlink (DL) may be used for the transmission path, or send direction, from a base station to a mobile station. The expression Uplink (UL) may be used for the transmission path, or send direction, in the opposite direction, i.e. from a mobile station to a base station.
In UMTS Frequency Division Duplex (FDD) (also known as WCDMA, Universal Terrestrial Radio Access (UTRA) FDD, HSPA FDD), only 5 MHz channel bandwidth (BW) has been defined. This means that all carriers and all cells on a carrier operate over a 5 MHz bandwidth. The chip rate is also the same for all carriers and all cells i.e. 3.84 Mega chips per second (Mcps). However, in some cases the available frequency resources owned by operators cannot accommodate a 5 MHz UMTS FDD. The use of 5 MHz in such cases may also result in suboptimal spectrum usage, e.g. if the allocated channel bandwidth is larger than 5 MHz. On the other hand, the 5 MHz channel cannot be used for operating UTRA FDD over smaller bandwidths, e.g. 3 MHz.
To allow for a more efficient spectrum allocation and usage for UMTS FDD, the concept of scalable channel bandwidth is being studied in 3GPP. Support of scalable bandwidths will enable UMTS FDD in constrained spectrum scenarios where the available contiguous spectrum is less than 5 MHz or not a multiple of 5 MHz, either as standalone single-carrier UMTS FDD or as multi-carrier UMTS FDD.
Typical examples of scalable channel bandwidths for scalable UMTS operations are 7.5 MHz, 2.5 MHz, 1.25 MHz, 0.6125 MHz etc. The time scale of the signal transmitted on a scalable bandwidth needs to be adapted. More specifically it is scaled compared to that of the signal transmitted on the reference BW (i.e. 5 MHz legacy channel BW). This is achieved by proportionally scaling the chip rate. Therefore the chip rates for channel BWs of 7.5 MHz, 2.5 MHz, 1.25 MHz, 0.6125 MHz would be 5.74 Mcps, 1.92 Mcps, 0.96 Mcps and 0.48 Mcps respectively. In other words the corresponding scaling factors (K) to scale the chip rates with respect to the reference chip rate (i.e. legacy 3.84 Mcps) are 3/2, 1/2, 1/4 and 1/8 for 5.74 Mcps, 1.92 Mcps, 0.96 Mcps and 0.48 Mcps respectively.
In CDMA, the information rate of the signal transmitted on a channel depends upon the symbol rate, which in turn is derived from the chip rate and the spreading factor (SF). In S-UMTS the spreading factor a particular physical channel is expected to remain the same as in legacy UMTS (i.e. 3.84 Mcps). This means the information rate will reduce if S-UMTS channel BW is smaller than the legacy 5 MHz. In other words the same amount of information is transmitted over longer time period. For example for K=½ (i.e. 2.5 MHz) the HSDPA TTI will be increased from 2 ms to 4 ms assuming the same SF as in the legacy 5 MHz UMTS.
In UTRA FDD, the same chip rate (3.84 Mcps) is used in all cells on the same carrier and also on all carriers. In scalable UMTS (S-UMTS), the UTRA FDD will operate with different chip rates e.g. 3.84 Mcps, 1.28 Mcps etc. In UTRA Time Division Duplex (TDD), different chip rates are supported on different carriers.
In a S-UMTS deployment scenario, with different bandwidths of UMTS cells, more and new information about the UMTS cells has to be managed. This should be done in way that is compatible with existing UMTS solutions, and in a manner that is compatible and work with already existing UMTS functionality and services, which may already be in use by operators and/or end users. Without this, S-UMTS deployment may in practice be difficult or even impossible.